Beyond R-134a: What's Next for Mobile A/C Refrigerants?

In February, the U.S. Environmental Protection Agency issued final approval of HFO-1234yf as a refrigerant for air conditioners in new cars and light trucks.

(Above) The receiver-dryer's moisture indicator gives a quick visual cue about the refrigerants's condition. (Below) When a compressor overheats, the rubber end-caps can melt right off (right).

It eventually will likely replace R-134a, commonly used today as the A/C refrigerant in cars, trucks, and other vehicles. Some expect it will be seen in medium- and heavy-duty commercial trucks within the next decade.

A product of Honeywell and Dupont, HFO-1234yf is a more environmentally friendly alternative to R-134a. HFO-1234yf was developed in part to help auto makers comply with a European Union ban on mobile refrigerants with a global warming potential greater than 150 in new car and light-truck platforms starting this model year.

GWP is a value used to compare different greenhouse gases that trap heat in the atmosphere. R-134, with a GWP of 1,400, has an atmospheric life of 13 years. HFO-1234yf has a GWP of 4 and an atmospheric life of 11 days.

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The ban on R-134a does not apply to vehicles in North America, nor are there any regulatory timetables to require low-GWP refrigerants in cars or trucks. The EPA decision means that vehicle manufacturers in the United States can use HFO-1234yf to help comply with rules requiring a 40 percent improvement in overall U.S. fleet average vehicle fuel economy by 2016. The EPA awards regulatory credit for the improved environmental performance of the new refrigerant.

For instance, General Motors announced it will use HFO-1234yf in Chevrolet, Buick, GMC and Cadillac models sold here beginning with the 2013 model year. The company said the use of HFO-1234yf "will help GM vehicles significantly exceed its targets under the new regulations."

Other alternatives

HFO-1234yf won out over other alternatives (including CO2) as the likely refrigerant of choice for the global mobile vehicle industry. It has been selected due to its ultra-low global warming and ozone depleting potential and its compatibility and near-equal performance with R134a in conventional vehicle HVAC systems.

"Other than requiring a different lubricating oil for the compressor, it provides a near 'drop-in' replacement alternative," says John Bracey, vice president of engineering for Bergstrom, which markets Kysor-brand HVAC parts.

Some system changes are required if the system cannot tolerate the approximate 5 percent performance loss inherent with R1234yf, Bracey notes. "For automotive systems, and an increasing number of commercial vehicle systems, this loss in efficiency correlates to a negative impact on fuel economy, which needs to be accommodated through other system changes."

One of the alternatives considered was CO2 refrigerant, which has the benefits of being non-flammable, non-toxic, and readily available. But the drawbacks of CO2 are amplified in heavy-duty vehicles, including high operating pressures and a need for metal hoses, seals and lines, says Gary Hansen, vice president at Red Dot Corp., which specializes in heavy-duty mobile climate control systems and has been very involved in this issue.

Virtually every component, from compressors to heat exchangers, would have to be redesigned to handle the higher pressures.

"A CO2-based A/C system operates at eight to 10 times the operating pressure, making it extremely difficult to contain from leaking in a mobile vehicle environment," Bracey says.

What can truck owners expect?

Currently only the European Union has passed legislation requiring the elimination or R134a in new car and light truck platforms released after 2011.

"The commercial vehicle industry in general has thus far focused on improving the containment and prevention of leaks in mobile vehicle A/C systems and as of now, have deemed that to be an adequate current solution," says Bergstrom's Bracey.

Several other factors, however, will influence what becomes the refrigerant of choice for medium- and heavy-duty trucks, he says. "Future legislation can definitely have an impact as fuel economy standards, CO2 emission limits, etc. creep into commercial vehicles. Current production capacity of R1234yf is not capable of supplying a total global demand and therefore costs are extremely high. Conversely, as no new capacity is being added for R134a, costs are rising as well. Ultimately cost versus benefit will drive the adoption."

Red Dot's Hansen expects we could see A/C systems using HFO-1234yf in new trucks within the next five to 10 years, barring regulatory action.

"Tests show that 1234yf has 5 percent less cooling capacity than 134a, but we can optimize the A/C system with some simple modifications," Hansen says. "A 1234yf system should look and perform very much like a 134a system today."

This last point is critical, Hansen says.

"If you ask a heavy-duty truck owner what he wants from his A/C system, greenhouse gas reduction is probably not going to be on the list. In fact, he wants it to be effective, reliable, easy to service, and not raise the cost to operate his vehicle," Hansen says. "As we transition to a new refrigerant, the best change we can make to the A/C system is one the customer won't even notice."

While HFO-1234yf will not require major modifications of HVAC systems, it is not intended as a drop-in replacement for R-134a. There will be different charge ports for HFO-1234yf to help prevent mixing up the refrigerants.

For vehicles that will be using HFO-1234yf, service shops and technicians may need to purchase or use new equipment, says the Society of Automotive Engineers. These may include recovery/recycle/recharge equipment, refrigerant identifiers and leak detection equipment. The new refrigerant is also mildly flammable, so precautions used with other flammable materials such as gasoline or oil are required.

Cool PM

Like any system on the truck, preventive maintenance is important. The best way to avoid big repair bills is to make A/C maintenance a year-round effort.

- Whenever you have a truck in for scheduled maintenance, check the moisture indicator on the receiver-dryer's sight glass. In general a dryer should be replaced once a year or every time the A/C system is opened.

- Keep filters clean and installed.

- Clean out the condenser so it is free of debris and contamination. But a high-pressure hose can damage fins and disrupt the airflow across the condenser, so be careful when you clean the grille area.

- Repair any damaged fins.

- Inspect the system for proper compressor belt tension and clutch voltage.

- One reason trucks repeatedly experience short A/C clutch or compressor life is low voltage at the clutch coil lead wire. Poor ground wire connections are an obvious source - but some truckers are tapping into the electrical system to power hotel loads, which can steal the voltage an A/C clutch needs to do its job. So when testing voltage, re-create the full demand.

- All electrical connections should be kept clean. Install dielectric grease in any connectors that are frequently exposed to rain and road wash.

- Always replace O-rings and seals when a connection is broken.

- In the case of a compressor failure, the system should be flushed and the system components back-flushed to remove any potential compressor debris from clogging system heat exchangers or expansion devices.